High Keyhole Limpet Shell, Diodora alta
High Keyhole Limpet Shell, Diodora alta. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size: 1.5 cm (0.6 inches) x 1.0 cm (0.4 inches) x 0.8 cm (0.3 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The High Keyhole Limpet Shell, Diodora alta (C.B. Adams, 1852) is a gastropod mollusk that is a member of the Fissurellidae Family of Keyhole Limpets. The genus Diodora is one of forty-five genera in this family, and there are ninety-five species in this genus. They are known in Mexico as Lapa Alta.
Description: High Keyhole Limpet Shells are oval in outline and have a high conical profile. The posterior slope is convex and the anterior slope is flat. The exterior is sculpted with a rough cancellate pattern that extends to the margin. The orifice is small, ovate, and set forward on the shell. The posterior edge of the callus is flattened. The exterior is white to gray in color, with gray, black, or brown radial bands. The interior is glossy white. High Keyhole Limpet Shells reach a maximum length of 1.5 cm (0.6 inches).
Habitat and Distribution: High Keyhole Limpet Shells are found attached to rocks from the low intertidal zone to a depth of 35 m (115 feet). They are a subtropical to tropical Eastern Pacific species that are found in are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from the west coast of the Baja Peninsula.
Ecology and Behavior: High Keyhole Limpet Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Most other species in Family Fissurellidae are herbivorous grazers that feed primarily on algae, though some are spongivores or detritivores. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.
Synonym: Fissurella alta.